Butanol is an important industrial chemical with a variety of applications, such as use as a fuel additive, as a blend component to diesel fuel, as a feedstock chemical in the plastics industry, and as a foodgrade extractant in the food and flavor industry. Each year 10 to 12 billion pounds of butanol are produced by petrochemical means. As the projected demand for butanol increases, interest in producing butanol from renewable resources such as corn, sugar cane, or cellulosic feeds by fermentation is expanding.
In a fermentative process to produce butanol, in situ product removal advantageously reduces butanol inhibition of the microorganism and improves fermentation rates by controlling butanol concentrations in the fermentation broth. Technologies for in situ product removal include stripping, adsorption, pervaporation, membrane solvent extraction, and liquid-liquid extraction. In liquid-liquid extraction, an extractant is contacted with the fermentation broth to partition the butanol between the fermentation broth and the extractant phase. The butanol and the extractant are recovered by a separation process, for example by distillation. In the recovery process, the butanol can also be separated from any water, non-condensable gas, and/or fermentation by-products which may have been removed from the fermentation broth through use of the extractant.
Copending U.S. patent application Ser. No. 12/478,389 filed on Jun. 4, 2009, discloses methods for producing and recovering butanol from a fermentation broth, the methods comprising the step of contacting the fermentation broth with a water immiscible organic extractant selected from the group consisting of C12 to C22 fatty alcohols, C12 to C22 fatty acids, esters of C12 to C22 fatty acids, C12 to C22 fatty aldehydes, and mixtures thereof, to form a two-phase mixture comprising an aqueous phase and a butanol-containing organic phase.
Copending U.S. Provisional Patent Application Nos. 61/168,640; 61/168,642; and 61/168,645; filed concurrently on Apr. 13, 2009; and 61/231,697; 61/231,698; and 61/231,699; filed concurrently on Aug. 6, 2009, disclose methods for producing and recovering butanol from a fermentation medium, the methods comprising the step of contacting the fermentation medium with a water-immiscible organic extractant comprising a first solvent and a second solvent, the first solvent being selected from the group consisting of C12 to C22 fatty alcohols, C12 to C22 fatty acids, esters of C12 to C22 fatty acids, C12 to C22 fatty aldehydes, and mixtures thereof, and the second solvent being selected from the group consisting of C7 to C11 alcohols, C7 to C11 carboxylic acids, esters of C7 to C11 carboxylic acids, C7 to C11 aldehydes, and mixtures thereof, to form a two-phase mixture comprising an aqueous phase and a butanol-containing organic phase.
Copending U.S. Provisional Patent Application Nos. 61/225,659 and 61/225,662, filed concurrently on Jul. 15, 2009, disclose processes for separating butanol from a mixture comprising butanol, water, a water-immiscible organic extractant, and optionally a non-condensable gas.
Processes for recovering butanol from a butanol-containing extractant phase obtained by in situ product removal from a fermentation broth continue to be sought. Economical processes for recovering butanol substantially free of water and of the extractant are desired. Also desired are separation processes which are energy efficient and provide high purity butanol product having little color. Butanol recovery processes which can be run for extended periods without equipment fouling or repeated shutdowns are also sought.